Conventional general cosmetic sheets have been manufactured to contain essence including nutrients such as natural extracts, proteins, and vitamins on a nonwoven fabric so as to have functions such as whitening, wrinkle reduction, water supply, relief from skin troubles, allowance of skin elasticity, and antibiotics.
However, since the conventional cosmetic sheets are manufactured on the basis of a nonwoven fabric, sufficient adhesion is not achieved at the interface contacting the skin, and thus effective ingredients cannot be sufficiently transferred to the deep part of the skin. In addition, an excessive amount of essence has been added to improve adhesive strength or power with respect to the skin.
Therefore, when a user makes an action actively with a conventional cosmetic sheet attached to the skin, the cosmetic sheet may fall or flow down use due to the self-weight of the cosmetic sheet itself and the excessive essence may flow out, to thus result in uncomfortable and unpleasant feeling and also cause a loss of the essence. In addition, wearing a cosmetic sheet may often make it difficult for a wearer to take daily activities, and thus the wearer may have to lie down during the time of wearing the cosmetic sheet.
In order to overcome such disadvantages, hydrogel cosmetic sheets have recently been widely used. Since the hydrogel cosmetic sheet is excellent in the feeling of fit, a wearer who wears the hydrogel cosmetic sheet may perform daily activities, but the hydrogel cosmetic sheet is so thick to cause limited adhesion and to result in inconveniences of having to remove the hydrogel cosmetic sheet separately after the lapse of the wearing time.
In recent years, research on electrospinning is being actively conducted as a method of forming nanofibers having a diameter of less than 1 μm. The nanofibers produced by the electrospinning method are formed in a laminate structure having a three-dimensional pore structure at the same time of manufacture, and thus can be applied to various fields including industrial and medical fields such as various filter materials, ultra-light functional clothes utilizing moisture permeability and water resistance, biomedical materials using pore characteristics and large surface areas, and inorganic materials and carbon materials through post-processing.
In particular, in the field of cosmetics, nanofibers can provide much larger skin contact areas than conventional nonwoven fabrics, and can be spun at room temperature and atmospheric pressure. Accordingly, various functional materials are mixed with a spinning solution, and the spinning solution mixed with the various functional materials is spun, to then be manufactured in the form of nanofibers mounted with the functional materials at the same time of spinning.
As disclosed in Korean Patent Application Publication No. 10-2011-080066, a conventional cosmetic sheet has been proposed in which a double-layered nanofiber layer is formed on a nonwoven fabric, and the double-layered nanofiber layer is surface-treated with plasma. However, this technology includes a process of making a composite of the nanofiber layer on the nonwoven fabric and a secondary process such as a plasma treatment, to thus cause not only a problem of increasing a process cost, and but also cause inconveniences in wearing the cosmetic sheet and making an action due to the addition of the nonwoven fabric.
In addition, a process such as lamination, thermal bonding, or ultrasonic bonding using a chemical adhesive or the like is required to make a composite of the nonwoven fabric and the nanofiber layer. When the adhesive or the like is not used, peeling between the nonwoven fabric and the nanofiber layer may happen due to the functional essence or moisture.
Furthermore, the nanofibers of the double-layered structure are spun in the form of a core/shell, in which the core portion is made of polyurethane or the like, and the shell portion contacting the skin is made of biodegradable polymers to minimize the trouble with the skin. However, in the case that 100% of the residual solvent is not removed due to the use of the toxic solvent, there is a problem of secondary contamination by the residual solvent.
Particularly, since most of the biodegradable polymers used in the conventional art are required to be hydrophilized through a plasma treatment due to the hydrophobic properties of the biodegradable polymers, there may have problems of causing an increase in the process cost as well as causing deterioration of the functional material.